Emily Brockway is the flower girl Eliza Dolittle, center, in the Opera North production of “My Fair Lady.”

LEBANON, N.H. — “My Fair Lady,” based on George Bernard Shaw by Lerner and Loewe, is one of a handful of American musicals that can genuinely be called masterpieces — and Opera North’s production, which opened Saturday, made it pretty clear just why, sticking mighty close to the original.

“My Fair Lady” is based on Shaw’s play “Pygmalion,” in which Prof. Henry Higgins bets Col. Pickering that by teaching the cockney flower girl Eliza Dolittle proper English he can pass her off as a duchess at the Embassy Ball. The music and lyrics are among Frederick Loewe and Alan Jay Lerner’s best, but it is the libretto — word-for-word Shaw’s — that makes it invincible and fresh to every new generation.

Opera North’s production, conducted by artistic director Louis Burkot and directed by Catherine Doherty, followed the original, missing nothing but streamlining the scene changes, reducing it to two and a half hours. More importantly, every minute was entertaining — and compelling.

The cast was an interesting mix of theater and opera singers and therein was the Saturday opening night performance’s only obvious problem. Mark Womack played Higgins beautifully with verve, sarcasm and a beautiful baritone, and with real dimension. Emily Brockway was a delightful Eliza, spunky and charming, with a gorgeous lyrical soprano.

And the two were a delight together. Brockway, making her entrance as the lady Eliza at the ball, was breathtaking — and Womack her perfect foil.

Womack, an opera and theater singer, and Brockway, a theater artist, were among a few who were individually miked and the result was often a synthetic sound. Actually, in the case of Brockway, the amplification was unnoticeable when she was singing but obvious when she was speaking, It was always noticeable with Brockway. As this was opening night, this problem may well be fixed.

Two performers that weren’t miked, and certainly didn’t need it, were Jonathan Tetelman as Freddy Eynsford-Hill, Eliza’s suitor, and Branch Fields as Alfred P. Dolittle, Eliza’s father. In fact, with his first song, “On the Street where You Live,” Tetelman’s gorgeous tenor and lyrical delivery, though not as loud as the miked voices, brought an enthusiastic ovation.

With his powerful and experienced operatic bass, Fields was appropriately charismatic as the senior Dolittle. On top of that, without detracting from anyone else, he lit up the stage with this wonderful character.

Wonderful comic portrayals were given by Christopher Flockton as Col. Pickering and Dorothy Stanley as Mrs. Higgins. The chorus was excellent, and the children — unusually — added to the production’s charm.

Doherty’s stage direction was appropriately spare and nuanced, with a few extra charming touches, allowing the Shaw to come forth. Burkot led the excellent full orchestra in a spirited and nuanced performance. Susan Lamontagne’s choreography was a bit on the square side, but effective.

The minimal but attractive and ever-moving staging was by Karen Koslowski, effectively lit by John Bartenstein; beautiful period costumes, notably in the Ascot scene, were by Collette Benoit.

These days it takes an opera company to mount a golden era musical like this, with full orchestra, large casts and lavish staging. And Opera North’s fine production makes it obvious why “My Fair Lady” is frequently called the “perfect musical.”

All performances are at the Lebanon Opera House, 51 N. Park St. in Lebanon, N.H. All are accompanied by full orchestra, and “La Traviata” is sung in the original Italian with English surtitles. For tickets, call (603) 448-0400, or go online to www.lebanonoperahouse.org. For information, visit www.operanorth.org.